Atticus is a loving father because he is involved in his children’s lives but not overbearing, he makes sure to teach his children important life lessons, and he always treats them fairly.
First of all, Atticus is involved in his children’s lives, but not to the point of being too controlling.
Jem and I, plus Calpurnia our cook. Jem and I found our father satisfactory: he played with us, read to us, and treated us with courteous detachment. (ch 1)
Although the children often complain about his being old and feeble, he also gives them chances to experience life. He is not a helicopter parent. He does not allow his children to play the Boo Radley game or build a snowman that looks like a neighbor, but other than that the kids pretty much have the run of the neighborhood.
This does not mean that Atticus ignores his children. He actually is very concerned with making sure they have a strong moral compass. He tells Scout that she needs to learn empathy in order to get along with people.
You never really understand a person until you consider things from his point of view…until you climb into his skin and walk around in it. (ch 3)
He wants Scout to understand that other people have different perspectives, and she needs to understand them.
Atticus also teaches Jem, and Scout, a lesson in courage. He makes Jem go to Mrs. Dubose’s house to read to her after he ruins her flowers when she insults his father for defending Tom Robinson.
I wanted you to see what real courage is, instead of getting the idea that courage is a man with a gun in his hand. It's when you know you're licked before you begin but you begin anyway… (ch 11)
Atticus wants his kids to understand that there are going to be challenges in life, but you have to be strong mentally and physically.
Atticus also treats his children fairly. When Uncle Jack spanks Scout for fighting with her cousin Frances, Atticus tells him that children should be treated fairly and told the truth.
So far I've been able to get by with threats. Jack, she minds me as well as she can. Doesn't come up to scratch half the time, but she tries. (ch 9)
Atticus listens to his children. He is firm, but fair. He is a good, loving father.